Sector X is part of a trio of nebulae that appear in the shape of a letter, itself formed in the shape of a giant X. Scientists are sure that it is not a natural formation but thus far have been unable to explain how it was formed. Travel through the sector is ill-advised, as electromagnetic pulses from the nebula interfere with navigational systems and critical engine components, making flights near the area hazardous.
During the course of the Lylat Wars, Cornerian spies reported that Andross created a secret research facility in Sector X, but then all contact with them was lost. Remote scanning revealed the existence of a debris field, but nothing more could be found out that way.
Unable to conclude what had happened General Pepper ordered the Star Fox team to investigate. They discovered that the base had been destroyed by Spyborg, whose artificial intelligence had malfunctioned and caused it to attack the base. Fighting through the Venomian Army and defense systems that were still active after Spyborg's attack, Fox McCloud succeeded in reaching the giant construct and destroying it before its rampage could continue elsewhere. The team also discovered the existence of an artificial Warp Portal generator, which allowed instantaneous travel across Lylat to Sector Z.
In an attempt to intercept Star Wolf, the Star Fox team were sent by General Pepper to investigate the ruined base and make sure that Andross was not using the warp for his plans. When the team arrived at the base, they found it in ruins and began searching for the cause of the destruction. The team flew through the base until they came to a fork in the destruction. Flying to the left brought Fox McCloud to the four warp gates that Andross had built. Shooting all four triggered the warp and Fox and his team flew through a warp zone to Sector Z.
Continuing to fly right forced Fox to deal with the remaining enemy forces in the area. On this path, Fox fought the Spyborg, also known as the HVC-09 experiment that Andross was working on. The experiment had failed and resulted in the destruction of the base. Fox destroyed the robot and Leon Powalski would be smacked by part of the Spyborg and Star Wolf are forced to go to Titania to save him while the Star Fox intercept them.
Sector X is only playable in Star Fox Command. Falco Lombardi (and eventually, Katt Monroe) are trapped within the sector, surrounded by Anglar forces. After fighting them off, they are confronted by Pigma Dengar, who was believed to have died after merging with the Aparoids during Star Fox Assault. However, Falco and Katt defeat him. Falco on his way to meet Fox McCloud, telling him they prepared to defeat the Anglar Emperor by attacking the home base on Venom.
- In Star Fox 64, the coloration of Sector X is blue, while it's red in Star Fox Command. Sector X was originally blue, as shown in pre-release images.
- Star Fox 64 3D revised Sector X's appearance a second time; it now consists of an orange X shape surrounded by blue and orange gas.
- It is believed that the reason that the planet Solar never fully cooled was due to its being in the center of the three sectors.